Recently, the necessity of electronic control in construction machinery is increasing more and more. Especially, in the electronic control in the construction machinery, an electro-hydraulic main control valve with an electro proportional pressure reducing valve (EPPRV) may be used. Thus, risk of failure in the electro proportional pressure reducing valve may be increased compared with a conventional hydraulic main control valve, and accordingly risk management at the failure may become very important.
When the electro proportional pressure reducing valve fails, a secondary pressure outputted from the electro proportional pressure reducing vale may be generated smaller than an external command signal, may not be generated, or may be generated a maximum pressure value. In the former case, an actuator of a vehicle may not move or move slowly, while in the latter case, the actuator may move fast even though the actuator should not move.
In this case, it may be more dangerous for the actuator to move inadvertently or unintentionally, and occasionally an operator may manipulate a safety lever or push an engine emergency button. However, these actions are at the operator's discretion, and in some case, it may be too late to prevent danger in advance.
Further, when the safety lever is manipulated, because the vehicle does not operate to move, it may be difficult to get out the danger zone for the breakdown repair service. Accordingly, in a conventional system where some or all operations are electrically controlled, because when some of the electro proportional pressure reducing valves fail, the whole vehicle does not operate to move or action, there are difficult problems to detect failure and take safety.